For example, Japanese Patent Application Laid-Open Publication No. 2014-107592 (Patent Document 1), Japanese Patent Application Laid-Open Publication No. 2013-535922 (Patent Document 2) and Japanese Patent Application Laid-Open Publication No. 2008-78893 (Patent Document 3) disclose a configuration including two switching devices on which an inter-device link aggregation group (hereinafter, abbreviated as LAG) is set. In the system of the Patent Document 1, when a frame is received, a bridge frame for learning is exchanged between the two switching devices. Thus, as shown in FIG. 4 of the Patent Document 1, the two switching devices completely synchronize the address tables including the information of the ports on which the inter-device LAG is not set.
In addition, also in the system of the Patent Document 2, by making a communication between two switching devices, the two switching devices completely synchronize the address tables including the information of the ports on which the inter-device LAG is not set as shown in Table 7 and Table 8 of the Patent Document 2. In the system of the Patent Document 3, when one box-type switch receives a frame, it transmits a MAC (Media Access Control) learning request packet containing a MAC address (SA), VLAN information and a port number to the other box-type switch.